1. Field of the Invention
The present invention relates to a device for supplying a paper to a printer for use with a computer, wordprocessor and plotter, etc. and other various printers.
2. Description of the Prior Art
In a printer for use with a computer, wordprocessor and plotter, etc., there has been widely employed a paper formed with a pair of rows of feed apertures at both side edges thereof for a recording paper for recording characters and figures to be printed by the printer. Each row of the feed apertures is arranged a predetermined distance from each side edge of the paper on a straight line along the side edges of the paper, and the feed apertures are formed at equal intervals.
A device for supplying this kind of paper to the printer is generally provided with a pair of tractors having endless belts at positions corresponding to both sides of the paper along a path of the paper to be supplied to the printer. Each endless belt is provided with a row of plural feed pins projecting outwardly therefrom and arranged at the same intervals as those of the feed apertures of the paper. Each endless belt encompasses a driving sprocket and a driven sprocket or a guide member in a loop. When the driving sprocket is rotated, a plurality of the feed pins present at a straight portion of the endless belt between the driving sprocket and the driven sprocket or the guide member are brought into engagement with the feed apertures of the paper to thereby feed the paper along a straight feed path to the printer.
FIGS. 8 and 9 show a typical example of such a tractor of a paper feeding device as mentioned above. FIG. 8 is a sectional view of the paper feeding device arranged at one side edge of the paper, and FIG. 9 is a transverse sectional view taken along the line IX--IX in FIG. 8. A frame of the paper feeding device is constructed by fixing a first side frame 11 to a second side frame 12 by a suitable means. A driving sprocket 15 is supported to a shaft which is rotatably mounted on and supported between both frames 11 and 12. The first side frame 11 is integrally formed with a belt guiding member 47, and a free end of the belt guiding member 47 abuts against the second side frame 12. The belt guiding member 47 has a U-shape composed of straight portions formed by parallel straight surface portions 49 and 50 and an arcuate portion formed by an arcuate surface portion 48 having an outer peripheral surface smoothly connected to the outer peripheral surfaces of the straight surface portions 49 and 50 and having a radius substantially equal to that of the outer circumferential surface of the driving sprocket 15. The belt guiding member 47 is located in such a manner that an extension line from the outer peripheral surface of the straight surface portions 49 and 50 are in tangential contact with the outer circumferential surface of the driving sprocket 15. Thus, the endless belt 1 is stretchedly mounted on the outer circumferential surface of the driving sprocket 15, the straight surface portions 49 and 50 and the arcuate surface portion 48 of the belt guiding member 47 in a loop. When the driving sprocket 15 is rotated in a direction shown by an arrow in FIG. 8, internal teeth formed on the inner peripheral surface of the endless belt 1 are brought into mesh with external teeth formed on the outer circumferential surface of the driving sprocket 15 to thereby move the endless belt 1. Accordingly, a portion of the endless belt 1 located along the outer circumference of the driving sprocket 15 is driven to run counterclockwise along an arcuated feed path 2. Then, the endless belt 1 is guided by the belt guiding member 47. That is a portion of the endless belt 1 located along a straight surface portion 50 of the belt guiding member 47 is guided to run straight along the straight feed path 5, and a portion of the belt located along the arcuate surface portion 48 of the belt guiding member 47 is guided to run arcuately along the arcuate feed path 3. Then, a portion of the endless belt 1 located along a straight surface portion 49 is guided to run straight along the straight feed path 4. The feed pins 6 are projected from the outer peripheral surface of the endless belt 1 in perpendicular relationship thereto, and are arranged at the same intervals as those of the feed apertures formed at the side edge portion of the paper. During the operation, the feed pins 6 provided at the portion of the endless belt 1 located on the straight surface portion 49 and moving along the straight feed path 4 are brought into engagement with the feed apertures of the paper to thereby feed the paper in parallel relationship to the straight surface portion 49.
In this kind of paper feeding device, the widths of the arcuate surface portion 48 and the straight surface portions 49 and 50 of the belt guiding member 47 are substantially equal to the width of the endless belt 1 as shown in FIG. 9. Accordingly, during the running of the endless belt 1, both side edges of the endless belt 1 are slidingly contacted with opposite inner side surfaces of the first and second frames 11 and 12. With this arrangement, the portion of the endless belt 1 running along the straight feed path 4 is prevented from being laterally slipped. Accordingly, the engagement of the feed pins 6 at the portion of the endless belt 1 running along the straight feed path 4 with the feed apertures of the paper may be stabilized to ensure the feeding of the paper.
However, as the inner peripheral surfaces of the portions of the endless belt 1 running along the arcuate feed path 3, the straight feed paths 4 and 5 are slidingly contacted with the arcuate surface portion 48 and the straight surface portions 49 and 50 of the belt guiding member 47 over the entire width thereof, there occurs a sliding friction due to the sliding contact between the endless belt 1 and the belt guiding member 47. The more the endless belt 1 is stretched longitudinally so as to prevent a slack of the endless belt 1, the greater a surface pressure between the inner peripheral surface of the endless belt 1 and the arcuate surface portion 48 of the belt guiding member 47, thus causing an increase in sliding friction. To cope with this problem, it is necessary to increase a driving force of a driving motor for driving the driving sprocket 15 by an amount corresponding to an increase in the sliding friction. Accordingly, the installation cost and the running cost are increased with an increase in the driving force of the driving motor.